Phase I: Patients who have not previously received imatinib mesylate receive oral imatinib mesylate daily on days 1-35. Patients who have previously received imatinib mesylate for at least 28 days receive oral imatinib mesylate on days 22-35. All patients receive cytarabine IV over 2 hours every 12 hours on days 29-32. Patients with more than 5% residual blasts in bone marrow on day 28 receive a second course in the absence of disease progression or unacceptable toxicity. Cohorts of 3-6 patients receive escalating doses of cytarabine until the maximum tolerated dose (MTD) is determined. The MTD is defined as the dose preceding that which 2 of 6 patients experience dose-limiting toxicity.